What material is used to make the x-ray tube envelope that encloses a vacuum?

The x-ray tube envelope is typically made from Pyrex glass. This material is chosen for its excellent thermal properties, which are critical in managing the heat generated during x-ray production. Pyrex glass can withstand high temperatures and is also resistant to thermal shock, making it ideal for the intense operating conditions within the x-ray tube.

Using a vacuum inside the envelope is essential to prevent the electrons generated at the cathode from colliding with air molecules, which could degrade the efficiency of x-ray production and lead to unwanted scattering or absorption of x-rays. Additionally, Pyrex glass is transparent to x-rays, which allows the generated x-rays to pass through the envelope and reach the desired target area without significant absorption or attenuation.

The other materials listed are not suitable for the envelope’s design and function. Gadolinium alloy, Kovlar composite, and tungsten alloy have different properties and uses that do not align with the requirements needed for an effective x-ray tube envelope.